This invention relates generally to meander line slow wave structures and more particularly to such a structure which includes frequency selective attenuators.
Meander line slow wave structures utilized in combination with microwave devices are well known; however, such a structure is poorly matched at frequencies near the edge of the stop band which occurs above the normal operating frequency of the device employing the structure. As a result, undesirable high frequency oscillations have a tendency to build up in an injected beam crossed-field amplifier or traveling wave tube using a meander line slow wave structure. Heretofore, band edge oscillations were avoided either by limiting the tube current to a value below the start oscillation current or by making the slow wave structure dispersive so that the waves at the band edge are not synchronous with the electron beam. This resulted in a limitation either in the peak power or instantaneous bandwidth capability of the device.
Accordingly, it is the object of the present invention to inhibit band edge oscillations in a microwave device utilizing a meander line slow wave structure.
It is another object of the invention to provide a meander line slow wave structure which attenuates waves at frequencies near or within the stop band of the slow wave structure.
It is a further object of the invention to provide a broadband delay line suitable for incorporation in a high power microwave signal amplifier.
It is yet another object of the invention to provide a broadband delay line suitable for incorporation in a high power injected beam or emitting sole crossed-field amplifier which is adapted to attenuate frequencies near the edges of the pass band where undesired oscillations are likely to occur.
These and other objects are achieved by the placement of attenuating material in the form of side absorber bar type elements located adjacent the sides of a meander line slow wave structure where the attenuating material is preferably comprised of a beryllium oxide and silicon carbide ceramic composition which ranges between 60% silicon carbide and 40% beryllium oxide and vice versa. In the preferred embodiment, a 60% silicon carbide-40% beryllium oxide composition provides maximum attenuation at operation in the 10 GHz region. The side absorbers adjacent the delay line are additionally adapted to accommodate metallic top plate absorbers as well as nichrome films and slotted side rings in various configurations.